The present invention is a cyclonic system for processing fragmentary material to produce one or more end products having substantially uniform fragment size and/or aerodynamic buoyancy. Because aerodynamic buoyancy is related to moisture content, the cyclonic processing system may be used for drying moisture bearing fragmentary material.
Many industrial and agricultural processes yield fragments that are either too wet, too large or too varied in size, density, or composition to be of great utility. Of particular interest are post-consumer fragmentary materials gathered in recycling efforts, which are typically formed of more than one substance. Separating out the constituent substances from a mass of multi-substance fragments permits the separate collection and reuse of the substances.
An interesting example of a fragmentary material having nonuniformities that reduce its utility is provided by "hog fuel," as that term is used in the lumber industry. In this instance "hog fuel" is actually a mixture of wooden chips and bark that is typically a waste product of lumber mills. Hog fuel is typically fed into a "hog fuel boiler," to produce steam for use in various lumber and paper mill operations
Although the hog fuel is typically predried in a continuous feed rotary drum dryer, hog fuel boilers are nevertheless plagued by hog fuel moisture and fragment size inconsistency. A wetter than usual mass of hog fuel or a large clump of saw dust mixed into the hog fuel can extinguish the boiler fire.
An example of multi-substance fragments is provided by plastic one quart oil containers gathered for recycling. Typically the exterior of a plastic oil container bears a heat set polymer label. The label is made of a different type of polymer from the container so that the label must be separated from the container in order for an apparatus to separately collect the two different polymers for reuse. The containers must also be washed of oil residue and dried in order to avoid contaminating either polymer end product with oil or water.
Unfortunately, the above described tasks present a great challenge to one using the current technology. The drying potentially could be performed by a continuous feed rotary drum dryer. Rotary drum dryers, however, generate waste air that typically contains particles that should be removed before discharge into the atmosphere. This necessitates the use of pollution control equipment and the acquisition of a permit from the local pollution control agency. The particles also hamper efforts to recirculate the air back into the dryer as they tend to jam the recirculating air blower and contaminate the fragments being dried.
The separation of the constituent substances of the plastic oil containers is typically performed by cutting up the fragments and forcing the resultant subfragments against a wire mesh that catches the larger size subfragments, which are typically composed of the container polymer, and passes the smaller label subfragments. Unfortunately, the wire mesh frequently becomes clogged, thereby requiring replacement, which causes great expense and difficulty.
A patent search found no references to the use of cyclonic equipment that could be practically used to address the above noted problems in the processing of hog feed or plastic oil containers despite the fact that cyclonic equipment is fairly common in the pollution control field. A number of references describe cyclonic devices in which the fragmentary material falls through an air vortex and exits from the bottom of the device. None of the bottom exit device references, however, appear to teach the suspension of fragments in the vortex of the bottom-exit device.
Fragmentary materials that are lighter than water, such as plastic, however, become lighter still as they dry. Consequently, a bottom exit cyclonic device cannot dry lighter-than-water material to a uniform dryness because lighter-than-water material will rise in the vortex as its progressively reduced moisture content translates into increased aerodynamic buoyancy thereby avoiding a bottom exit. A bottom exit cyclonic device could be configured so that lighter-than-water material would fall quickly out of the device. This would, however, not permit much drying time and would not create a uniform aerodynamic buoyancy (i.e. dryness) in its product.
In another prior art device fragments are driven upwards and guided in a helical path by a helical baffle before entering a chamber in which they descend and exit. There is no indication, however, that any uniformity of dryness is introduced into the fragmentary mass or that the fragments are ever suspended in a vortex.
An additional reference found in the search teaches a columnar separator device in which fragments are lofted in a column by an upward draft of air and separated according to their buoyancy by a vertically spaced sequence of exit hoods and chutes. A columnar separator has only a limited precision, however, due to the jostling of the fragments in the upward draft of air. Moreover, because this device is not cyclonic it would be difficult to adapt it to effect physical changes to fragments because without suspending fragments in a vortex there is not much processing time.
U.S. Pat. No. 5,565,164, which shares co-inventor John C. Goehner with the present application, describes a cyclonic densifyer in which fragments of thermoplastic polymer are introduced into a vortex where they are softened by heat and broken and re-agglomerated until they form into fairly uniform pellets that are compact enough to precipitate from the vortex.
What is therefore needed but not yet available is a fragmentary material processing apparatus and method in which the fragments remain suspended in a vortex until reaching a predetermined aerodynamic buoyancy and/or fragment size. Among other purposes this apparatus and method is needed for drying moisture bearing fragments until a predetermined moisture results. An apparatus and method is also needed for milling, separating and mixing fragmentary material.